1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to demodulation techniques capable of demodulating a Frequency Shift Keyed (FSK) and/or Amplitude Shift Keyed (ASK) received signal.
2. Description of the Related Art
Related art demodulation circuits that are capable of demodulating both FSK and ASK received signals are generally one of two types. A first type of circuit includes two dedicated demodulators, namely a first dedicated ASK demodulator and a second dedicated FSK demodulator, as well as a control switch for selecting an output of either the FSK or ASK demodulator. Examples of such demodulator circuits are known from CA-A-2306846, EP-A-1589714, and US-A-2005/0063491.
A second type of demodulation circuit includes an FSK demodulator and an ASK demodulator, and a logic circuit. Based on results of the demodulation from the two demodulators, the logic circuit selects the valid one. Alternatively, the logic circuit may decide whether to execute demodulation with the second demodulator based on a result from the first demodulator. An example of such a demodulation circuit is known from EP-A-1187346.
Such circuits involve significant hardware resources, occupy significant die space when implemented in an integrated circuit, and/or have a high computation load in order to implement both types of demodulation in parallel or in series.
Both types of demodulation circuit may perform poorly when demodulating a poor quality or damaged FSK signal in which one of the FSK tones may be of low amplitude such as the tone being close to the noise floor. Such a signal is difficult to decode by a related art FSK demodulation technique, and would also not be recognised as a true ASK signal. Such a poor quality FSK signal is not uncommon in remote control applications, because a transmitter will usually be a miniaturized circuit that may be of low cost, low complexity, or have poor operating tolerances or low transmission power. The problem may be compounded when the signal is transmitted or received in a noisy wireless environment.
Although not directed to a dual FSK/ASK capability, reference may be made to the FSK-specific demodulators described in published French patent application Nos. 2846814, 2846815, 2846825 and 2859336. These patent applications are directed to improved reception and demodulation of a wireless FSK signal in a noisy environment.